Simplest method of disabling ping response is to add an entry in /etc/sysctl.conf file. If the Iptables flushes or stop server will start responding to ping responses again. I suggest the following entry in your /etc/sysctl.conf file

net.ipv4.icmp_echo_ignore_all = 1

this will tell kernel to not respond any ping response, after this run sysctl -p on shell to implement the changes without reboot.